The objective of this proposal is the development of a hand-held imaging probe for preoperative and intra operative localization of Sentinel Lymph Nodes (SLNs). The proposed probe design is a small scintillation camera with intrinsic spatial resolution of approximately 1 mm with a 2 cm x 2 cm physical field of view. The function is to image distributions of 140 keV gamma-rays either prior to surgery or during surgery. If capable of identifying the SLN prior to surgery the patient may be spared the surgical procedure of invasive lymph node biopsy. The use of the probe follows Lymphoscintigraphy whereby a radioactive colloid is followed dynamically with a conventional gamma camera to the lymph node basin that serves the diseased tissue. The first node in the basin (the SLN) is a strong indicator of whether the cancer has spread so the aim is to biopsy that node. The imaging probe will be the first device used in the operating room with imaging capabilities for real-time precise and unambiguous localization of the SLN. Among the innovative features of the imaging probe will be several interchangeable collimators that allow the user to rapidly change the field of view, spatial resolution and gamma-ray sensitivity of the probe. This versatility is important for this application as SLNs are of variable size and depth. The probe will also operate in non-imaging mode and meet the performance standards of existing non-imaging probes whose use in this field is growing. An attractive feature of the device developed here is its cost. It will offer imaging capability at the same cost of currently available non-imaging probes. PROPOSED COMMERCIAL APPLICATIONS: This project will result in an imaging probe to greatly facilitate the localization of the Sentinel Lymph Node during the staging of melanoma and breast cancer, among other potential tumor types. The imaging probe offers great advantages over the currently employed non-imaging probes at the same cost. The dynamic field of Sentinel Node Scintigraphy is growing in acceptance and scope. Many hospitals routinely use Lymphoscintigraphy and could enhance the procedure with this probe. The imaging probe developed here, at no extra cost to existing non-imaging probes, will provide physicians with a more functional instrument that can carry the Sentinel Node technique further and faster.